JPH1093244A - Multilayer silicon nitride circuit board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a multilayer silicon nitride circuit board, which has an superior heat radiating property and which can be reduced in size, while increasing areas of the mounting section and the circuit-constituting section, and has improved heat resisting cycle and high reliability. SOLUTION: A multilayer circuit board is provided with a plurality of silicon nitride substrates 10a, 10b of a high thermal conductivity and metal boards 3, 4, 5 joined to the silicon nitride substrates 10a, 10b of a high thermal conductivity. Each of the silicon nitride substrates 10a, 10b of a high thermal conductivity contains 1.0-17.5wt% of rare earth elements in terms of oxides, total 1.0wt% or less (including 0wt% which is the limit of detection) of impurity anode ion elements, including Li, Na, K, Fe, Ca, Mg, Sr, Ba, Mn, and B, and has a coefficient of thermal conductivity of at least 60w/m.k. In this multilayer circuit board, a plurality of the silicon nitride substrates 10a, 10b of a high thermal conductivity are partly overlapped through the metal boards 3, 4, 5.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multilayer silicon nitride circuit board useful as a semiconductor mounting board, a semiconductor package, and the like. The present invention also relates to a multilayer silicon nitride circuit board having improved heat dissipation, structural strength and heat cycle resistance.

[0002]

2. Description of the Related Art In recent years, a ceramic circuit in which a metal plate (metal circuit plate) such as a copper plate is joined to a ceramic substrate as a substrate for mounting semiconductor components handling relatively high power such as a power transistor module and a switching power supply module. A substrate is used.

[0003] In the manufacturing process of the ceramic circuit board as described above, the joining method of the ceramic substrate and the metal plate punched into a predetermined shape includes Ti, Zr, Hf, and N.
b) a method using an active metal brazing material containing 1 to 10% of an active metal such as Ag-Cu brazing material (active metal method), a tough pitch electrolytic copper containing 100 to 1000 ppm of oxygen as a metal plate, A ceramic substrate and a copper plate are directly joined using copper oxidized to a thickness of 10 μm,
A so-called direct bonding method (DBC method: direct bonding copper method) and the like are known.

For example, in the direct joining method, first, a copper circuit board having a thickness of 0.3 to 0.5 mm stamped into a predetermined shape is formed.
0.6 to 1.0 mm thick made of aluminum oxide (Al ₂ O ₃ ) sintered body or aluminum nitride (AlN) sintered body
Heated is disposed in contact with the ceramic substrate, the bonding interface to produce a eutectic liquid phase of Cu-Cu ₂ O, after wetting the surface of the ceramic substrate in the liquid phase by cooling and solidifying the liquid phase The ceramic substrate and the copper circuit board are directly joined. A ceramic circuit board to which such a direct bonding method is applied has a strong bonding strength between the ceramic substrate and the copper circuit board, and can be miniaturized and mounted with a simple structure that does not require a metallization layer or a brazing material layer. And the manufacturing process can be shortened.

[0005]

However, in a ceramic circuit board in which a metal plate is joined to a ceramic substrate by the above-described direct joining method, active metal method, or the like, the thickness of the metal plate is set to 0.1 mm so that a large current can flow. Since the thickness is 3 to 0.5 mm, there is a problem that the reliability against the heat history is poor. That is, when a ceramic substrate and a metal plate having significantly different coefficients of thermal expansion are joined, a thermal stress due to the difference in thermal expansion is generated due to a cooling process after the joining or the addition of a cooling / heating cycle. This stress exists as a compressive and tensile residual stress distribution on the ceramic substrate side near the joint, and the main residual stress mainly acts on the ceramic portion adjacent to the outer peripheral end of the metal plate. The residual stress may cause cracks in the ceramic substrate, cause a dielectric strength failure, or cause peeling of the metal plate. Further, even if cracks do not occur in the ceramic substrate, the ceramic substrate has an adverse effect of reducing its strength.

[0006] With the recent increase in the density and integration of semiconductor elements, miniaturization of semiconductor modules and electronic components themselves has been promoted. Under such circumstances, the semiconductor mounting substrate is required to be reduced in size, and in order to achieve high mounting, an increase in the area of a mounting portion and a circuit configuration portion is required.

However, in most conventional ceramic circuit boards, only one main surface of the ceramic substrate is used as a mounting surface. Although it is necessary to increase the size of the ceramic substrate itself, when the size of the ceramic substrate is increased, there arises a problem that the ceramic substrate is likely to be warped when the copper circuit board is joined. Further, simply increasing the size of the ceramic substrate is contrary to the demand for miniaturization of the mounting substrate and the electronic component itself.

As described above, in the conventional ceramic circuit board, in order to increase the area of the mounting portion and the circuit component portion, the size of the ceramic substrate must be increased. This causes problems such as inviting electronic components and contradicting the demand for miniaturization of electronic components. Also, with the diversification of semiconductor elements, the characteristics required for a semiconductor mounting substrate and a semiconductor package are also diverse, and it is required to satisfy those various requirements.

On the other hand, high integration and high output of the semiconductor element,
With an increase in size, there is an increasing technical demand for a circuit board structure capable of efficiently dissipating heat generated from an element to the outside and a high-strength circuit board structure capable of withstanding thermal stress. Therefore, an attempt was made to use a silicon nitride (Si ₃ N ₄ ) substrate having higher strength than a conventional alumina (Al ₂ O ₃ ) substrate as a ceramic substrate. However, Si ₃ N ₄
Substrates have excellent mechanical strength such as toughness, but their thermal conductivity is significantly lower than that of aluminum nitride substrates.Therefore, they are practically used as components of circuit boards for semiconductors that require heat dissipation. Not.

[0010] On the other hand, although the aluminum nitride substrate has higher thermal conductivity and lower thermal expansion characteristics than other ceramic substrates, it does not provide satisfactory mechanical strength, so that the mounting of the circuit board is difficult. The circuit board is easily damaged by the slight pressing force and impact force added in the process,
In some cases, the manufacturing yield of a semiconductor device is significantly reduced.

For this reason, in the conventional multilayer ceramic circuit board, it has become an essential requirement that the thickness of each ceramic substrate be increased. FIG. 3 is a cross-sectional view showing the structure of such a conventional multilayer ceramic circuit board 1. The multilayer ceramic circuit board 1 shown in FIG. 3 has two ceramic substrates 2a and 2b made of an AlN sintered body having a large thickness and a high thermal conductivity.
In addition, a copper plate 3 is bonded to the upper surface of the ceramic substrate 2b, and a metal plate 5 as a back copper plate is integrally bonded to the lower surface of the ceramic substrate 2a.
A semiconductor element 7 is mounted on a predetermined position of the copper plate 3 by soldering, and the semiconductor element 7 and an electrode portion of the copper plate 3 are electrically connected by bonding wires 8.

As described above, in the conventional multilayer ceramic (AlN) circuit board 1, the ceramic substrates 2a and 2b having a large thickness in order to increase the resistance to cracking.
Therefore, the size of the power module is increased, which makes it difficult to reduce the size of the power module. In addition, the manufacturing cost of the ceramic substrate is greatly increased. In addition, since the thickness of the substrate is increased, even when an AlN substrate having a high thermal conductivity is used, the thermal resistance is increased, and there is a problem that good heat dissipation cannot be obtained as expected.

SUMMARY OF THE INVENTION The present invention has been made to address such problems, and has excellent heat dissipation properties, can be reduced in size while increasing the area of a mounting portion and a circuit component portion, and can be further improved in heat cycle resistance and the like. It is an object of the present invention to provide a multilayer silicon nitride circuit board having improved reliability and improved reliability.

[0014]

According to a first aspect of the present invention, there is provided a multilayer silicon nitride circuit board, comprising: a rare earth element having an oxide content of 1.0 to 17.5% in terms of oxide; Li, Na, K, Fe, Ca, Mg,
It contains Sr, Ba, Mn, and B in a total of 1.0% by weight or less, preferably 0.3% by weight or less (including 0% by weight as a detection limit), and has a heat conductivity of 60 w / mk or more. A plurality of high thermal conductive silicon nitride substrates, and a metal plate bonded to the high thermal conductive silicon nitride substrates, wherein the plurality of high thermal conductive silicon nitride substrates are multilayered via the metal plates. It is characterized in that it has a portion which is formed.

According to another aspect of the present invention, there is provided a multi-layer silicon nitride circuit board containing a rare earth element in an amount of 1.0 to 17.5% by weight in terms of an oxide. A ratio of the crystalline compound phase in the grain boundary phase to the whole grain boundary phase is 20%.
A plurality of high thermal conductive silicon nitride substrates, preferably 50% or more, and a metal plate bonded to the high thermal conductive silicon nitride substrate, wherein the plurality of high thermal conductive silicon nitride substrates are It is characterized by having a multilayered portion via the metal plate.

In a preferred embodiment of the above-described multilayer silicon nitride circuit board of the present invention, the metal plate is bonded to the high thermal conductive silicon nitride board by a direct bonding method. And a form in which the metal plate is bonded to the high thermal conductive silicon nitride substrate by an active metal method.

The silicon nitride substrate having high thermal conductivity used in the present invention has a rare earth element content of 1.0 to 1 in terms of oxide.
7.5% by weight, Li, N as impurity cation element
a, K, Fe, Ca, Mg, Sr, Ba, Mn, and B in a total content of 1.0% by weight or less, preferably 0.3% by weight or less (including 0% by weight as a detection limit). It is composed of

The content range of the rare earth element oxide of 1.0 to 17.5% by weight is, of course, a mathematical expression, but the lower limit of the content is 1.0% by weight.
And an upper limit of 17.5% by weight.
Hereinafter, the same applies to other component ranges.

In another embodiment, the high thermal conductive silicon nitride substrate is formed by converting a rare earth element to an oxide in an amount of from 1.0 to 17.
5% by weight, comprising a silicon nitride crystal phase and a grain boundary phase, wherein the ratio of the crystalline compound phase in the grain boundary phase to the entire grain boundary phase is 20% or more, preferably 50% or more. May be formed.

It is particularly preferable to use a lanthanoid element as the rare earth element in order to improve the thermal conductivity.

Further, the high thermal conductive silicon nitride substrate may be constituted so as to contain 1.0% by weight or less of aluminum nitride or alumina. Further, 1.0% by weight or less of alumina and 1.0% by weight or less of aluminum nitride may be used in combination.

The high thermal conductive silicon nitride substrate used in the present invention is made of Ti, Zr, Hf, V, Nb, Ta,
At least one selected from the group consisting of Cr, Mo, W
It is preferable to contain the seed in an amount of 0.1 to 3.0% by weight in terms of oxide. This Ti, Zr, Hf, V, Nb, T
At least one selected from the group consisting of a, Cr, Mo, and W can be contained as an oxide, carbide, nitride, silicide, or boride by being added to the silicon nitride powder.

Further, the method of manufacturing a silicon nitride substrate having high thermal conductivity used in the present invention is characterized in that oxygen is not more than 1.7% by weight, and Li, Na, K, Fe, Ca,
Mg, Sr, Ba, Mn, B in total of 1.0% by weight or less, preferably 0.3% by weight or less, containing 90% by weight or more of α-phase silicon nitride and having an average particle size of 1.0 μm or less. Rare earth elements are converted to oxides in silicon nitride powder in an amount of 1.0 to
A raw material mixture containing 17.5% by weight or less and, if necessary, at least one of alumina and aluminum nitride added at 1.0% by weight or less is molded to prepare a molded body. After the obtained molded body is degreased, Atmospheric pressure sintering at a temperature of 1800 to 2100 ° C, and a cooling rate of the sintered body from the sintering temperature to a temperature at which a liquid phase formed at the time of sintering by the rare earth element solidifies is set to 100 ° C or less per hour. And gradually cooled.

In the above method, at least one of alumina and aluminum nitride is preferably added to the silicon nitride powder in an amount of 1.0% by weight or less.

Further, Ti, Z are added to the silicon nitride powder.
oxides of r, Hf, V, Nb, Ta, Cr, Mo, W;
At least one selected from the group consisting of carbides, nitrides, silicides, and borides may be added in an amount of 0.1 to 3.0% by weight.

According to the above manufacturing method, a grain boundary phase containing a rare earth element or the like is formed in the silicon nitride crystal structure, the porosity is 2.5% or less, the thermal conductivity is 60 W / m · K or more, and A silicon nitride substrate having a point bending strength of 650 MPa or more at room temperature and excellent in both mechanical properties and heat conduction properties is obtained.

The silicon nitride powder used as the main component of the sintered body used in the above manufacturing method has an oxygen content of 1.7% by weight or less in consideration of sinterability, strength and thermal conductivity. Preferably 0.5-1.5% by weight, Li, Na,
Α-phase silicon nitride in which the total content of impurity cation elements such as K, Fe, Mg, Ca, Sr, Ba, Mn, and B is suppressed to 1.0% by weight or less, preferably 0.3% by weight or less. Containing 90% by weight or more, preferably 93% by weight or more, and having an average particle size of 1.0 μm or less, preferably 0.4 to
A fine silicon nitride powder of about 0.8 μm can be used.

By using a fine raw material powder having an average particle diameter of 1.0 μm or less, a dense high thermal conductive silicon nitride substrate having a porosity of 2.5% or less even with a small amount of a sintering aid. Can be formed, and the possibility that the sintering aid impairs the heat conduction characteristics is reduced.

Further, Li, Na, K, Fe, Ca, Mg,
Since the impurity cation elements of Sr, Ba, Mn, and B are substances that hinder thermal conductivity, the content of the impurity cation element must be as follows in order to secure a thermal conductivity of 60 W / m · K or more. It can be achieved by setting the total to 1.0% by weight or less. In particular, for the same reason, the content of the impurity cation element is preferably not more than 0.3% by weight in total.
More preferred. Here, the silicon nitride powder used for obtaining a normal silicon nitride sintered body includes, in particular, Fe, C
a, Mg are contained in a relatively large amount, so that Fe, C
The total amount of a and Mg is a measure of the total content of the impurity cation element.

In the high thermal conductive silicon nitride substrate used in the present invention, the content of the impurity cation element cannot be completely 0% by weight in a mathematical sense. Therefore, the content of the impurity ion element specified in the present invention substantially includes 0% by weight as a detection limit.

Further, by using a silicon nitride raw material powder containing 90% by weight or more of α-phase silicon nitride which is superior in sinterability as compared with β-phase type, a high-density silicon nitride substrate can be formed. Can be manufactured.

The rare earth elements to be added to the silicon nitride raw material powder as a sintering aid include Ho, Er, Yb, Y,
Oxides such as La, Sc, Pr, Ce, Nd, Dy, Sm, and Gd, or substances that become these oxides by sintering operation alone or in combination of two or more oxides are included. Good, but especially holmium oxide (Ho ₂ O
₃ ) Erbium oxide (Er ₂ O ₃ ) is preferred.

In particular, by using Ho, Er, and Yb, which are lanthanoid elements as rare earth elements, sinterability or high thermal conductivity is improved, and sufficiently dense sintering can be achieved even in a low temperature range of about 1850 ° C. Solidification is obtained. Therefore, the effect of reducing the equipment cost and running cost of the firing apparatus can be obtained. These sintering aids are
It reacts with the silicon nitride raw material powder to form a liquid phase and functions as a sintering accelerator.

The amount of the sintering aid to be added is in the range of 1.0 to 17.5% by weight based on the raw material powder in terms of oxide.
When the addition amount is less than 1.0% by weight, the sintered body is insufficiently densified. In particular, when the rare earth element is an element having a large atomic weight such as a lanthanoid element, a relatively low strength is obtained. A sintered body having a relatively low thermal conductivity is formed. on the other hand,
If the added amount exceeds 17.5% by weight, an excessive amount of grain boundary phase is generated, and the thermal conductivity and strength start to decrease. It is particularly desirable to set the content to 4 to 15% by weight for the same reason.

Further, Ti, Zr, Hf, V, Nb, T
The oxides, carbides, nitrides, silicides, and borides of a, Cr, Mo, and W promote the function of the sintering accelerator of the rare earth element, and also have the function of strengthening the dispersion of Si _{3 in the} crystal structure. It is intended to improve the mechanical strength of the N ₄ sintered body, and particularly, compounds of Hf and Ti are preferable. When the added amount of these compounds is less than 0.1% by weight, the effect of the addition is insufficient, while when the added amount exceeds 3.0% by weight, the thermal conductivity and mechanical strength and electric breakdown are caused. Since the strength is reduced, the amount of addition is in the range of 0.1 to 3.0% by weight. In particular, it is desirable that the content be 0.2 to 2% by weight.

The compounds such as Ti, Zr, and Hf also function as a light-shielding agent that imparts opacity by coloring the silicon nitride sintered body to a black color. Therefore, in particular, when manufacturing a circuit board on which an integrated circuit or the like which easily malfunctions due to light is mounted, it is desirable to appropriately add the compound such as Ti and the like to obtain a silicon nitride substrate excellent in light shielding properties.

Further, in the above-mentioned manufacturing method, alumina (Al ₂ O ₃ ) as another optional additive component plays a role of promoting the function of the sintering accelerator for the rare earth element, This has a remarkable effect when sintering. When the addition amount of Al ₂ O ₃ is less than 0.1% by weight, sintering at a higher temperature is required. On the other hand, when the addition amount exceeds 1.0% by weight, an excessive amount of grain boundaries is required. Since a phase is formed or a solid solution starts to be formed in silicon nitride to cause a decrease in heat conduction, the amount of addition is set to 1% by weight or less, preferably 0.1 to 0.75% by weight.
In particular, in order to ensure good performance in both strength and thermal conductivity, it is desirable that the amount of addition be in the range of 0.1 to 0.5% by weight.

When used in combination with AlN, which will be described later, the total amount thereof is desirably 1.0% by weight or less.

Aluminum nitride (AlN) as a further additive serves to suppress the evaporation of silicon nitride during the sintering process and to further promote the function of the rare earth element as a sintering accelerator. It is.

If the amount of AlN added is less than 0.1% by weight (less than 0.05% by weight when used in combination with alumina), sintering at a higher temperature is required, while
If the amount exceeds 0% by weight, an excessive amount of the grain boundary phase is generated, or the solid solution starts to be dissolved in silicon nitride to cause a decrease in thermal conductivity. % By weight. In particular, in order to ensure good performance in sinterability, strength, and thermal conductivity, it is desirable that the addition amount be in the range of 0.1 to 0.5% by weight. When used in combination with Al ₂ O ₃ , the addition amount of AlN is 0.05 to 0.5% by weight.
Is preferable.

The sintered body is manufactured so as to have a porosity of 2.5% or less because it greatly affects the thermal conductivity and strength. If the porosity exceeds 2.5%, it hinders heat conduction,
As the thermal conductivity of the sintered body decreases, the strength of the sintered body decreases.

The silicon nitride sintered body is systematically composed of silicon nitride crystals and a grain boundary phase, and the ratio of the crystalline compound phase in the grain boundary phase greatly affects the thermal conductivity of the sintered body. However, in the high thermal conductive silicon nitride substrate used in the present invention,
It is necessary that the content be 20% or more of the grain boundary phase, and more preferably 50% or more is occupied by the crystal phase. If the crystal phase is less than 20%, it is not possible to obtain a silicon nitride substrate having high heat conductivity of 60 W / m · K or more and having excellent heat radiation characteristics and high temperature strength.

Further, as described above, the porosity of the high thermal conductive silicon nitride substrate is set to 2.5% or less, and the crystal phase accounts for 20% or more of the grain boundary phase formed in the silicon nitride crystal structure. To achieve this, the silicon nitride compact is heated to a temperature of 1800
Pressure sintering is performed at a temperature of ℃ 2100 ° C. for about 2 to 10 hours, and the cooling rate of the sintered body immediately after the completion of the sintering operation is 100
It is important that the temperature is lowered to below ℃.

When the sintering temperature is lower than 1800 ° C., the densification of the sintered body is insufficient, the porosity becomes 2.5 vol% or more, and both the mechanical strength and the thermal conductivity decrease. On the other hand, when the sintering temperature exceeds 2100 ° C., the silicon nitride component itself tends to be vaporized and decomposed. Especially not pressure sintering,
When normal-pressure sintering is performed, decomposition and evaporation of silicon nitride starts at about 1800 ° C.

The cooling rate of the sintered compact immediately after the completion of the sintering operation is an important control factor for crystallizing the grain boundary phase, and when rapid cooling is performed such that the cooling rate exceeds 100 ° C./hour. Is that the grain boundary phase of the sintered body structure becomes non-crystalline (glass phase), the ratio of the liquid phase generated in the sintered body as a crystalline phase to the grain boundary phase is less than 20%, and the strength and thermal conductivity are reduced. Both will fall.

The temperature range in which the cooling rate should be strictly adjusted is a temperature range from a predetermined sintering temperature (1800 to 2100 ° C.) to a temperature at which a liquid phase produced by the reaction of the sintering aid solidifies. Is enough. Incidentally, the liquidus freezing point when using the sintering aid as described above is approximately 1600 to 15
It is about 00 ° C. The cooling rate of the sintered body at least from the sintering temperature to the above-mentioned liquid phase solidification temperature is set to 10
0 ° C. or lower, preferably 50 ° C. or lower, more preferably 2 ° C.
By controlling the temperature to 5 ° C. or less, 20% or more of the grain boundary phase can be obtained.
Particularly preferably, 50% or more becomes a crystalline phase, and a sintered body excellent in both thermal conductivity and mechanical strength can be obtained.

The high thermal conductive silicon nitride substrate used in the present invention is manufactured, for example, through the following process. That is, a predetermined amount of a sintering aid, a necessary additive such as an organic binder, and optionally Al ₂ O are added to the fine silicon nitride powder having the predetermined fine particle size and a small impurity content. _A raw material mixture is prepared by adding ₃ or an AlN or Ti compound, and then the obtained raw material mixture is molded to obtain a molded body having a predetermined shape. As a molding method of the raw material mixture,
A general-purpose mold pressing method, a sheet forming method such as a doctor blade method, and the like can be applied. Subsequent to the above molding operation, the molded body is heated at a temperature of 600 to 800 in a non-oxidizing atmosphere.
C. or in air at a temperature of 400 to 500.degree. C. for 1 to 2 hours to sufficiently remove the organic binder component added in advance and degrease. Next, the degreased molded body is subjected to atmospheric pressure sintering at a temperature of 1800 to 2100 ° C. for a predetermined time in an inert gas atmosphere such as nitrogen gas, hydrogen gas or argon gas.

The silicon nitride substrate manufactured by the above method has a porosity of 2.5% or less and 60 W / m · K (25 ° C.).
It has the above thermal conductivity and a three-point bending strength of 65 at room temperature.
It has excellent mechanical properties of 0 MPa or more.

The silicon nitride substrate obtained by adding high thermal conductivity SiC or the like to low thermal conductivity silicon nitride to have a thermal conductivity of 60 W / m · K or more as a whole of the sintered body is within the scope of the present invention. Is not included. However, the thermal conductivity is 60 W /
m.K or higher silicon nitride sintered body with high thermal conductivity Si
Needless to say, a silicon nitride-based substrate in which C is compounded is included in the scope of the present invention.

The multilayer silicon nitride circuit board according to the present invention comprises:
A metal plate having conductivity is integrally bonded between the plurality of highly thermally conductive silicon nitride substrates manufactured as described above, the front surface, and, if necessary, the back surface using the direct bonding method or the active metal method. It is manufactured in multiple layers.

In the multilayer silicon nitride circuit board of the present invention, a plurality of high thermal conductive silicon nitride boards obtained by joining a metal plate such as a copper circuit board by a direct joining method or an active metal method are used.
It is multilayered via a metal plate. Therefore, by enabling a three-dimensional assembly, it is possible to reduce the size while increasing the area of the mounting portion and the circuit configuration portion, and to achieve a small size and high mounting.

In addition, by forming a high thermal conductive silicon nitride substrate having a metal plate such as a copper plate into a multilayer structure, not only can a package or the like be formed, but also a metal plate such as a copper plate can be used as a circuit component. In addition, the current loss can be improved as compared with the conventional multilayer package, and an effect that can be applied to a high-frequency semiconductor element, a large current semiconductor element, and the like can be achieved.

In particular, a high thermal conductive silicon nitride substrate having a significantly improved thermal conductivity in addition to the inherently high strength and toughness characteristics of a silicon nitride sintered body is used as a ceramic substrate. Heat generated from a heat-generating component such as a semiconductor element mounted on the substrate is quickly transmitted to the outside of the system via the high thermal conductivity silicon nitride substrate, so that heat dissipation is extremely good. In addition, since a silicon nitride substrate having high strength and toughness is used, a large amount of maximum deflection of the circuit board can be secured. For this reason, the circuit board does not suffer from tightening cracks in the assembly process, and it is possible to mass-produce semiconductor devices using the circuit board at a high production yield and at low cost.

Further, since the high thermal conductivity silicon nitride substrate has a high toughness value, cracks are less likely to occur at the joint between the substrate and the metal plate due to thermal cycling, and the heat cycle characteristics are significantly improved, and the durability and reliability are improved. A semiconductor device having excellent performance can be provided.

Since a silicon nitride substrate having a higher thermal conductivity is used, even when a semiconductor element for high output and high integration is mounted, deterioration of thermal resistance characteristics is small and excellent. Exhibits heat dissipation.

In particular, the mechanical strength of the high thermal conductive silicon nitride substrate itself is excellent. Therefore, when the required mechanical strength characteristics are kept constant, the substrate thickness is larger than when other ceramic substrates are used. It is possible to further reduce the size. Since the substrate thickness can be reduced, the thermal resistance value can be further reduced, and the heat radiation characteristics can be further improved.
Further, since the required mechanical characteristics can be sufficiently coped with even a thinner substrate than before, it is possible to further reduce the manufacturing cost of the substrate.

When only the conventional high thermal conductive aluminum nitride substrate is used as a constituent material of the circuit board, it is necessary to increase the thickness of the aluminum nitride substrate in order to secure a certain level of mechanical strength. However, in the multi-layer silicon nitride circuit board of the present invention, high heat dissipation and high strength characteristics are ensured at the same time mainly by the high thermal conductivity silicon nitride substrate having a small thickness. Therefore, the circuit board can be formed compact.

[0058]

Next, an embodiment of the present invention will be described.
A specific description will be given with reference to the following embodiments and the accompanying drawings. First, a high thermal conductive silicon nitride substrate used in the present invention will be described, and then, a multilayer silicon nitride circuit substrate using this high thermal conductive silicon nitride substrate as a ceramic substrate will be described.

First, various high thermal conductive silicon nitride substrates to be used as constituents of the multilayer silicon nitride circuit board of the present invention were manufactured by the following procedure.

That is, a silicon nitride raw material containing 1.3% by weight of oxygen and 0.15% by weight of the impurity cation element in total and containing 97% of α-phase type silicon nitride and having an average particle size of 0.55 μm. As shown in Tables 1 to 3, as shown in Tables 1 to ₃ , rare earth oxides such as Y ₂ O ₃ and Ho ₂ O ₃ as sintering aids, and Ti, Hf compounds, and Al ₂ O ₃ powders as needed. ,
AlN powder was added, and the mixture was wet-mixed in ethyl alcohol using a silicon nitride ball for 72 hours, and then dried to prepare raw material powder mixtures. Next, a predetermined amount of an organic binder was added to each of the obtained raw material powder mixtures, mixed uniformly, and then press-molded at a molding pressure of 1000 kg / cm ² to produce a large number of molded bodies having various compositions.

Next, each of the obtained compacts was degreased in an atmosphere gas at 700 ° C. for 2 hours.
After the densification sintering is performed under the sintering conditions shown in (1) to (3), sintering is performed until the temperature in the sintering furnace falls to 1500 ° C. by controlling the amount of electricity to a heating device attached to the sintering furnace. The sintered bodies were cooled by adjusting the cooling rates of the bodies so as to be the values shown in Tables 1 to 3, respectively, to prepare silicon nitride sintered bodies according to Samples 1 to 51, respectively. Further, the obtained sintered body was cut to obtain a high thermal conductive silicon nitride substrate having a predetermined shape with a thickness of 0.3 mm and 0.6 mm.

The average values of the porosity, the thermal conductivity (25 ° C.), and the three-point bending strength at room temperature were measured for the silicon nitride substrates according to Samples 1 to 51 thus obtained. Furthermore, the ratio of the crystal phase to the grain boundary phase was measured by X-ray diffraction for each silicon nitride substrate, and the results shown in Tables 1 to 3 below were obtained.

[0063]

[Table 1]

[0064]

[Table 2]

[0065]

[Table 3]

As is clear from the results shown in Tables 1 to 3, in the silicon nitride sintered bodies according to Samples 1 to 51, the raw material composition and the amount of impurities were appropriately controlled, and the densified sintering was performed as compared with the conventional example. Since the cooling rate of the sintered compact immediately after completion is set lower than before, the crystal phase is included in the grain boundary phase, and the higher the proportion of the crystal phase, the higher the heat conductivity and the higher the strength of the silicon nitride. An elementary substrate was obtained.

On the other hand, 1.3 to 1.5% by weight of oxygen and 0.13 to 1.5%
A raw material powder having an average particle size of 0.60 μm containing 0% by weight and containing 93% of α-phase type silicon nitride was used, and Y ₂ O ₃ (yttrium oxide) powder was added to the silicon nitride powder in an amount of 3%. To 6% by weight and 1.3 to 1.6% by weight of alumina powder
After shaping and degreasing the added raw material powder, sintering is performed at 1900 ° C. for 6 hours, and after sintering, furnace cooling (cooling rate:
(400 ° C. per hour). The thermal conductivity of the obtained sintered body was as low as 25 to 28 W / m · K, which was close to the thermal conductivity of a silicon nitride sintered body manufactured by a conventional general manufacturing method.

Next, the thickness of each of the obtained samples 1 to 51 was set to 0.
A multi-layer silicon nitride circuit board is formed by integrally bonding metal plates to both sides of two high thermal conductive silicon nitride substrates of 3 mm and 0.6 mm using a direct bonding method or an active metal method to form a multilayer. Was manufactured.

FIG. 1 is a sectional view showing the structure of a multilayer silicon nitride circuit board according to one embodiment of the present invention.

In FIG. 1, two high thermal conductive silicon nitride substrates 10a and 10b are integrally joined via a copper plate 4 as a metal plate, and the surface of the high thermal conductive silicon nitride substrate 10b is A copper plate 3 is joined as a metal plate. On the other hand, a copper plate 5 is similarly bonded to the back surface of the high thermal conductive silicon nitride substrate 10a, and these form a multilayer silicon nitride circuit substrate 9A.

The copper plates 3, 4, and 5 in the multilayer silicon nitride circuit board 9A shown in FIG. 1 are directly joined to the high thermal conductive silicon nitride substrates 10a and 10b by a so-called DB method.
They are joined by the C method. It is preferable to use copper containing 100 to 3000 ppm of oxygen, such as tough pitch copper, as the copper plates 3, 4, and 5 when using such a DBC method. Can also be used. Instead of a single plate of copper or a copper alloy, a clad plate or the like with another metal member having at least a joint surface with the high thermal conductive silicon nitride substrates 10a and 10b may be used.

The copper plate 3 bonded to the surface of the high thermal conductive silicon nitride substrate 10b is to be a mounting portion for semiconductor components and the like, and is patterned into a desired circuit shape.
A semiconductor element 7 is soldered to a predetermined position of the copper plate 3, and an electrode portion of the semiconductor element 7 is electrically connected to an electrode portion of the copper plate 3 by a bonding wire 8. The copper plate 5 bonded to the back side of the high thermal conductive silicon nitride substrate 10a prevents warpage of the high thermal conductive silicon nitride substrate 10a at the time of bonding, and is divided into two parts from near the center. Almost High Thermal Conductivity Silicon Nitride Substrate 10
a is bonded and formed on the entire back surface. Copper plate 5 on the back side
May have a thickness the same as that of the copper plate 3 to be a mounting part for a semiconductor component or the like, but 70 to 90% of the thickness of the copper plate 3 may be used.
It is preferable to use a copper plate having a thickness of

Here, the multilayer silicon nitride circuit board 9A shown in FIG. 1 has two high thermal conductive silicon nitride substrates 10a,
The copper plates 3, 4, and 5 are joined to the base plate 10b by the DBC method. For example, as shown in FIG. 2, the copper plates 3, 4, and 5 are joined by the active metal method to form two high thermal conductive silicon nitride substrates 10a and 10b.
It may be a multilayer silicon nitride circuit board 9B bonded to 10b. The active metal method includes, for example, Ti, Zr, Hf,
Two high thermal conductive silicon nitride substrates 10 a and 10 b and a copper plate 3 are interposed via a brazing material layer 6 containing at least one active metal selected from Nb or the like (hereinafter referred to as an active metal-containing brazing material). 4 and 5 are joined. As the composition of the active metal-containing brazing material to be used, for example, an Ag-Cu eutectic composition (72 wt% Ag-28 wt% Cu) or a composition in the vicinity of the eutectic composition is mainly composed of an Ag-Cu brazing material or a Cu brazing material
For example, a composition in which at least one active metal selected from Ti, Zr, Hf, Nb and the like is added to 1 to 10% by weight is exemplified. In addition, in the active metal-containing brazing material, In
It can also be used by adding 0% by weight.

The multi-layer silicon nitride circuit board 9A shown in FIG.
As described above, those obtained by bonding the copper plates 3, 4, and 5 to the high thermal conductive silicon nitride substrates 10a and 10b by the DBC method can provide a simple structure, high bonding strength, and simplification of the manufacturing process. Having. Further, as shown in the multilayer silicon nitride circuit board 9B shown in FIG. 2, the copper plates 3, 4, and 5 bonded to the high thermal conductive silicon nitride substrates 10a and 10b by the active metal method have high bonding strength. In addition, since the active metal-containing brazing material layer 6 also functions as a stress relaxation layer, the reliability can be further improved. For this reason, it is preferable to select a joining method according to required characteristics, applications, and the like.

When a metal plate is bonded to the high thermal conductive silicon nitride substrates 10a and 10b by the active metal method,
Not only the copper plate but also various metal plates such as a nickel plate, a tungsten plate, a molybdenum plate, an alloy plate thereof, a clad plate (including a clad plate with a copper plate) and the like can be used according to the application.

The above-described multilayer silicon nitride circuit board 9 A
For example, it is manufactured as follows. That is, for example, an oxygen-containing copper plate such as tough pitch copper is processed into a predetermined shape (the copper plate 3 has a circuit pattern shape), and the obtained copper plates 3, 4, and 5 are processed into high thermal conductive silicon nitride substrates 10a and 10a.
b in contact with each other, and the melting point of copper (1356)
K) The copper plates 3, 4, and 5 are joined by heating at a temperature equal to or higher than the eutectic temperature of copper and copper oxide (1338K) or less to produce a multilayer silicon nitride circuit board 9A. When an oxygen-containing copper plate is used as the copper plate, the atmosphere for this heating is preferably an inert gas atmosphere.

The multilayer silicon nitride circuit board 9B in which metal plates are joined by the active metal method is manufactured, for example, as follows. First, the multilayer silicon nitride circuit board 9A
Similarly, copper plates 3, 4, and 5 having a predetermined shape are prepared. On the other hand, a paste made of the active metal-containing brazing material as described above is used as, for example, a high thermal conductive silicon nitride substrate 10a, 1a.
0b. The coating thickness of the brazing material layer is preferably such that the thickness of the brazing material layer 6 after the heat bonding is not too large in order to improve the thermal cycle characteristics.
Next, the copper plates 3, 4, and 5 are respectively laminated on the surfaces of the high thermal conductive silicon nitride substrates 10a and 10b to which the brazing material paste has been applied, and heat-treated at a temperature according to the brazing material used. A multilayer silicon nitride circuit board 9B is manufactured.

In the multilayer silicon nitride circuit boards 9A and 9B having the structure described above, the metal plates 3 such as a copper circuit board,
4 and 5 joined by direct joining method or active metal method 2
The high thermal conductivity silicon nitride substrates 10a and 10b are multi-layered via metal plates 3, 4 and 5. Therefore, by enabling a three-dimensional assembly, it is possible to reduce the size while increasing the area of the mounting portion and the circuit configuration portion, and to achieve a small size and high mounting.

The multi-layer of the high thermal conductive silicon nitride substrates 10a and 10b having the metal plates 3, 4 and 5 such as a copper plate makes it possible not only to form a package or the like but also to form a metal plate such as a copper plate. Is used as a circuit component, current loss can be improved as compared with a conventional multilayer package, and high-frequency semiconductor elements and large-current semiconductor elements can be handled.

Next, specific examples of the embodiment and evaluation results thereof will be described.

Example 1 First, samples 1 to 3 were used as high thermal conductive silicon nitride substrates.
A silicon nitride substrate according to No. 51 was oxidized in the air to form a 4 μm thick oxide layer (SiO ₂ layer) on the surface.
0.3mm and 0.6mm high thermal conductive silicon nitride substrates 10a and 10b having a thickness of 0.3 mm and a tough pitch copper (oxygen content: 300
ppm) of copper plates 3 and 4 having a thickness of 0.3 mm and a copper plate 5 having a thickness of 0.25 mm.

Then, as shown in FIG. 1, three copper plates 3 are formed on both sides of the high thermal conductive silicon nitride substrates 10a and 10b.
Nos. 4 and 5 were placed in direct contact with each other, and heated and joined in a nitrogen gas atmosphere at 1348 K to obtain a target multilayer silicon nitride circuit board 9A.

On the other hand, as a comparative example, instead of the high thermal conductive silicon nitride substrates 10a and 10b, as shown in FIG.
A multilayer aluminum nitride circuit board according to a comparative example was manufactured in the same manner as in Example 1 except that a and 2b were used.

The thus obtained multilayer silicon nitride circuit board according to Example 1 and the multilayer aluminum nitride circuit board of Comparative Example were subjected to a thermal cycle test (TCT: 233K ×
30 minutes + RT × 10 minutes + 398 K × 30 minutes as one cycle), and the rate of occurrence of cracks in the ceramic substrate was measured. As a result, the multilayer silicon nitride circuit board of Example 1 did not crack even after 100 cycles of TCT, whereas the multilayer aluminum nitride circuit board of the comparative example had a ceramic substrate of 5 to 100 cycles after 100 cycles of TCT. Cracks occurred in 9%.

Example 2 As heat-conductive silicon nitride substrates, high-heat-conductive silicon nitride substrates 10a and 10b having a thickness of 0.3 mm and 0.6 mm according to Samples 1 to 51 were prepared. Copper plates 3 and 4 having the same shape and a predetermined shape formed by press working and having a thickness of 0.3 mm and a copper plate 5 having a thickness of 0.25 mm were prepared.

Then, as shown in FIG. 2, In: Ag: C is formed on both surfaces of the high thermal conductive silicon nitride substrates 10a and 10b.
u: Ti = 14.0: 59.0: 23.0: 4.0 A paste of an active metal-containing brazing material having a composition of
After laminating and disposing the copper plates 3, 4, 5 via this coating layer,
Heating and bonding were performed in a nitrogen gas atmosphere to obtain a target multilayer silicon nitride circuit board 9B.

When a thermal cycle test was performed on the multilayer silicon nitride circuit board 9B obtained in this manner under the same conditions as in Example 1, the same good results as in Example 1 were obtained. It was confirmed that the reliability was excellent.

Further, according to the multilayer silicon nitride circuit boards 9A and 9B according to each of the above-described embodiments, the thermal conductivity has been significantly improved, in particular, in addition to the inherent high strength and toughness characteristics of the silicon nitride sintered body. High thermal conductive silicon nitride substrates 10a and 10b are used. Accordingly, heat generated from heat-generating components such as the semiconductor element 7 mounted on the substrate is quickly transmitted to the outside of the system through the silicon nitride substrates 10a and 10b having high thermal conductivity, so that heat dissipation is extremely good.

Further, since the high thermal conductivity silicon nitride substrates 10a and 10b having high strength and high toughness are used, the maximum deflection of the circuit board can be secured large. For this reason, the circuit board does not suffer from tightening cracks in the assembly process, and it is possible to mass-produce semiconductor devices using the circuit board at a high production yield and at low cost.

Further, the high thermal conductive silicon nitride substrates 10a, 1
0b has a high toughness value.
Provided is a semiconductor device in which cracks are less likely to occur at the joints between a and 10b and a metal circuit board or metal plates 3, 4, and 5, heat cycle characteristics are significantly improved, and durability and reliability are excellent. Can be.

Since the silicon nitride substrates 10a and 10b having a higher thermal conductivity are used, even when the semiconductor element 7 for high output and high integration is mounted, deterioration of the thermal resistance characteristic is not caused. Exhibits excellent heat dissipation.

In particular, since the mechanical strength of the silicon nitride substrate itself is excellent, when the required mechanical strength characteristics are fixed, the thickness of the substrate is more reduced than when other ceramic substrates are used. It becomes possible to reduce. That is, in the conventional multilayer ceramic circuit board, the thickness of the ceramic substrate is generally 0.6 to 1.0 mm, but by using the high thermal conductive silicon nitride substrate used in the present invention, It can be used even when the thickness is reduced to 0.1 to 0.6 mm. Since the substrate thickness can be reduced, the thermal resistance value can be further reduced, and the heat radiation characteristics can be further improved. In addition, since the required mechanical characteristics can be sufficiently coped with even a thinner substrate than before, the substrate manufacturing cost can be further reduced.

[0093]

As described above, according to the multilayer silicon nitride circuit board of the present invention, a plurality of high thermal conductive silicon nitride boards joined to a metal board such as a copper circuit board are connected via the metal board. It is multilayered. Therefore, by enabling a three-dimensional assembly, it is possible to increase the area of the mounting portion and the circuit configuration portion and reduce the size, and to achieve a small size and high mounting.

Further, since a silicon nitride substrate having high strength and toughness is used, a large amount of maximum deflection of the circuit board can be secured. For this reason, the circuit board does not suffer from tightening cracks in the assembly process, and it is possible to mass-produce semiconductor devices using the circuit board at a high production yield and at low cost.

[Brief description of the drawings]

FIG. 1 is a sectional view showing the structure of a multilayer silicon nitride circuit board according to one embodiment of the present invention.

FIG. 2 is a sectional view of a multilayer silicon nitride circuit board according to another embodiment of the present invention.

FIG. 3 is a sectional view showing the structure of a conventional multilayer ceramic circuit board.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Multilayer ceramic circuit board (multilayer AlN circuit board) 2a, 2b Ceramic substrate (AlN board) 3, 4, 5 Metal plate (metal circuit board, copper plate, copper back plate) 6 Active metal-containing brazing material layer 7 Semiconductor element (Si chip) 8) bonding wire 9A, 9B multilayer silicon nitride circuit board 10a, 10b high thermal conductive silicon nitride substrate

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Tsutsuyasu Komatsu 2-4, Suehirocho, Tsurumi-ku, Yokohama-shi, Kanagawa Prefecture Inside the Toshiba Keihin Plant (72) Inventor Kotoshi Sato 8-8 Shinsugita-cho, Isogo-ku, Yokohama-shi, Kanagawa Toshiba Yokohama Office

Claims (6)

[Claims] 1. The method according to claim 1, wherein the conversion of the rare earth element to oxide is 1.0 to 1.0.
17.5% by weight, Li, N as impurity cation element
Contains a, K, Fe, Ca, Mg, Sr, Ba, Mn, and B in total of 1.0% by weight or less (including 0% by weight as a detection limit), and has a thermal conductivity of 60 w / mk or more. A plurality of high thermal conductive silicon nitride substrates, and a metal plate bonded to the high thermal conductive silicon nitride substrate, wherein the plurality of high thermal conductive silicon nitride substrates are multilayered through the metal plate. What is claimed is: 1. A multilayer silicon nitride circuit board, comprising: 2. The high thermal conductive silicon nitride substrate is composed of Li, Na, K, Fe, Ca, M as impurity cation elements.
2. The multilayer silicon nitride circuit board according to claim 1, wherein the total content of g, Sr, Ba, Mn, and B is 0.3% by weight or less (including 0% as a detection limit). 3. The method according to claim 1, wherein the conversion of the rare earth element to oxide is 1.0 to 1.0.
A plurality of high thermal conductive silicon nitrides containing 17.5% by weight and comprising a silicon nitride crystal phase and a grain boundary phase, wherein the ratio of the crystalline compound phase in the grain boundary phase to the entire grain boundary phase is 20% or more; A high-thermal-conductivity silicon nitride substrate, and a metal plate joined to the high-thermal-conductivity silicon nitride substrate, wherein the plurality of high-thermal-conductivity silicon nitride substrates have a multilayered portion via the metal plate. Multi-layer silicon nitride circuit board. 4. The high thermal conductive silicon nitride substrate is composed of a silicon nitride crystal phase and a grain boundary phase, and the ratio of the crystalline compound phase in the grain boundary phase to the entire grain boundary phase is 50.
4. The multilayer silicon nitride circuit board according to claim 3, wherein 5. The multilayer silicon nitride circuit board according to claim 1, wherein the metal plate is bonded to the high thermal conductive silicon nitride substrate by a direct bonding method. 6. The multilayer silicon nitride circuit board according to claim 1, wherein the metal plate is bonded to the high thermal conductive silicon nitride substrate by an active metal method.